Metal forming

ABSTRACT

An upstanding hollow rivet is formed in a metal can end by pressurally engaging opposite sides of the can end with a pair of die elements, one of which is formed with a recess. The dies place a continuous zone of the can end under compressive stress sufficient to cause metal of the zone to be forcibly displaced into the die recess with consequent thinning of the compressed area whereby an integral rivet is formed which comforms to the size and shape of the die recess.

Mitten States Patent [1 1 Brown METAL FORMING [75] inventor: Omar L. Brown, Dayton, Ohio [73] Assignee: Ermal C. Fraze, Dayton, Ohio [22] Filed: June 18, 1965 [21] Appl. No.: 464,909

Related US. Application Data [63] Continuation-impart of Ser. No. 288,204, June 17,

1963, abandoned.

[52] US. Cl 113/121 C, 72/253, 72/352,

220/54 [51] Int, Cl ..1321d 51/38 [58] Field of Search 113/121, 116 FF, 121 R,

[56] References Cited UNITED STATES PATENTS 942,989 12/1909 Warren .1 72/256 1,413,284 4/1922 Maloney 72/256 2,106,647 l/1938 Neck 72/256 [451 May 28, 1974 2,909,281 10/1959 Koskinen 72/256 2,966,987 1/1961 Kaul 72/256 3,191,564 6/1965 Fraze 113/121 3,307,737 3/1967 Harvey et a1. 220/54 3,387,481 6/1968 Harvey et a1. 72/379 FORElGN PATENTS OR APPLICATIONS 590,720 7/1947 Great Britain 113/116 Primary Examiner-Lowell A. Larson Attorney, Agent, or Firm-Smyth, Roston and Pavitt 5 7 ABSTRACT An upstanding hollow rivet is formed in a metal can end by pressurally engaging opposite sides of the can end with a pair of die elements, one of which is formed with a recess. The dies place a continuous zone of the can end under compressive stress sufficient to cause metal of the zone to be forcibly displaced into the die recess with consequent thinning of the compressed area whereby an integral rivet is formed which comforms to the size and shape of the die recess.

7 Claims, 12 Drawing Figures METAL FORMING This application is a continuation-in-part of my copending application of the same title, Ser. No. 288,204 filed June 17, 1963, now abandoned.

This invention relates to metal forming operations and more particularly to methods for forming rivets used in attaching tear tabs to containers and especially can tops thereof, although the invention is not necessarily so limited.

An object of this invention is to provide a new method of forming a protuberance such as a hollow rivet in a sheet metal wall of a container.

Another object of this invention is to provide an improved method for forming a protuberance in a container, the protuberance to be used as a hollow rivet by which a tear tab may be attached to the container.

Still another object of this invention is the provision of a novel method for attaching tear tabs to sheet metal walls of containers.

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode of operation, as will become more apparent from the following description.

Referring to the drawings, FIG. 1 is a simplified perspective view of a can top to which a tear tab has been applied in accordance with this invention;

FIG. 2 is a schematic, cross-sectional illustration of a pair of die members and a can top blank used in the method of forming the can top of FIG. 1;

FIG. 3 is an enlarged view of a portion of the elements shown in FIG. 2 at a later stage in the operation thereof;

FIG. 3a is a fragmentary cross-sectional view showing how a scoring die may be employed to form a tear strip in the can top blank after a rivet of initial configuration has been formed in the blank;

FIG. 4 is a fragmentary cross-sectional view showing an apertured tab positioned on the can top and showing die means poised for deforming the hollow rivet into engagement with the tab;

FIG. 5 is a similar view showing how the die means deforms or heads the hollow rivet into its final configuration in engagement with the tab;

FIG. 6 is a sectional view similar to FIG. 3 showing how the lower die may be provided with a small central boss to facilitate the formation of the hollow rivet;

FIG. 7 is a sectional view showing how a different set of dies may be employed to form a hollow rivet;

FIG. 8 shows the hollow rivet formed by the dies shown in FIG. 7 and further shows the result of scoring the sheet metal blank;

FIG. 9 is a fragmentary plan view of the hollow rivet of initial configuration shown in FIG. 8 showing how the score line extends into the annular region where the metal is thinned around the base of the rivet;

FIG. 10 is a fragmentary sectional view showing how a special tab may be positioned for engagement by the hollow rivet and also showing die means poised for deforming the hollow rivet into engagement with the tab; and

FIG. 11 is a view similar to FIG. 10 showing the completion of the die operation for deforming or heading the hollow rivet into engagement with the tab.

Great difficulty has been experienced in attempting to mechanically attach tear tabs to containers, especially non-ferrous metal containers. Thee use of separate rivets or other fastening devices is generally undesirable. Forming a hollow rivet in the container itself has also been difficult, since the metal tends to shear or fracture when the hollow rivet is being initially formed or when the head is being subsequently formed on the hollow rivet. The steps taken in the past to avoid shearing or fracturing the metal have been time-consuming and expensive. In accordance with this invention, however, a hollow rivet may be formed in an aluminum or other metal container in one operation with a pair of die members, the hollow rivet being formed in the container metal itself. As will appear more fully below, the hollow rivet so formed is nearly ideally suited for its purpose.

Illustrated in FIG. I is a can top, generally designated 10, having the usual raised annular rim l2 and flat central portion 14. A tear tab 16 is shown attached to the can top 10 by a hollow rivet 18 which is integral with the central portion 14 of the can top. The tear tab 16 is adapted to tear away part of the central portion 14 bounded by score lines 20, which are only partially shown in FIG. 1. The score lines 20 may take any desired fonn adequate to enable part or all of the body portion 14 of the lid to be removed. Examples of such score lines are illustrated in US. Pat. No. 2,946,478.

In accordance with this invention, the shank of the hollow rivet 18 is fonned by placing an annular region of the can top blank under compression whereupon the hollow rivet protrudes from the area of the can top blank enclosed within the annular region. The extrusion of the hollow rivet may be accomplished by a pair of dies 22 and 24, illustrated in FIGS. 2 and 3.-The first or lower die 22 has a first working surface 26 with a central portion 28 offset towards the second die 24. The offset portion 28 may be termed a plateau and in this instance the plateau has a slightly convex surface 30 but, if desired, may have a planar surface. The second or upper die 24 has a planar working surface 32 and is formed with a central recess 34, the crosssectional area of which is the cross-sectional area of the desired hollow rivet. It is to be noted that the plateau 28 of the first or lower die 22 is of larger area than the cross sectional area of the recess 34.

In FIG. 2 a sheet metal blank for a can top, designated 14a, is supported between the working surfaces of the two dies 22 and 24. In practice the blank may initially rest on the plateau 28 of the lower die 22. The upper die 24 is forcefully and rapidly advanced or impacted against the upper surface of the blank 14a. Upon striking the upper surface of the blank, the sheet metal blank is placed under compression in a continuous zone around the area of the recess 34, the continuous zone being an annular zone where the working surface of the upper die 24 overlies the circumferential marginal portion of the plateau 28 of the lower die 22. At the same time, the remaining outer radial portion of the upper die surface 32 approaches the corresponding outer radial portion of the lower die surface 26 sufficiently to clamp the corresponding portion of the sheet metal against the lower die without compressing or deforming the blank.

As well known to those skilled in the art, metals tend to flow when subjected to compression and the sheet metal in the annular zone surrounding the recess 34 accordingly tends to flow in opposite radial directions. The resistance to outward radial flow is many times the resistance to inner radial flow, however, because on the one hand, the recess 34 provides a free space into which metal may flow and, on the other hand, solid metal blocks outward radial flow and especially so when the die surfaces cooperate to prevent thickening of the sheet metal in the outer radial region that surrounds the annular zone where the squeezing of the metal occurs. Consequently the metal displaced by the squeezing action in the annular zone is extruded radially inward into the recess 34 with the result that the sheet metal bows into domed-shaped configuration in the recess. This configuration, which is designated 18a in FIGS. 3, 3a and 4, may be termed the initial configuration of the hollow rivet, i.e., the configuration of the hollow rivet before it is deformed to form a head or bead.

It is important to note that the hollow rivet at its initial configuration 18a has a circumferential wall and a transverse end wall and the transverse end wall or the central area of the rivet is of substantially the same thickness as the original thickness of the blank 14a since this central area of the sheet metal has not been subjected to a squeezing action. Since the metal flows in the formation of the initial configuration 18a of the hollow rivet and does not bend there is little or no tendency for the metal to shear or crack around the edge or base of the hollow rivet. Conventional stop blocks or the like (not shown) may be used in a well known manner to limit the travel of the upper die 24 so as to avoid compressing the sheet metal surrounding the annular region where the metal is squeezed or thinned to form the hollow rivet.

One important advantage of the described method of forming a rivet is that the rivet may be formed close to the rim of the can top. Another advantage is that the rivet may be relatively small if desired.

After the dies shown in FIGS. 2 and 3 form a hollow rivet of initial configuration 18a, suitable dies are employed as indicated in FIG. 3a to form the previously mentioned score lines that define the tear strip that is to be removed by the tab 16. The dies shown in FIG. 3a produce a score line of the configuration in plan indicated in FIG. 9 where it may be seen that the score line 20 passes around three sides of a hollow rivet.

The die means shown in FIG. 3a comprises a lower die 36 shaped to conform to the underside of the can top blank 14a and an upper die 38 that has a cavity 40 dimensioned to clear the hollow rivet 18a. The upper die 38 is formed with an integral scoring element 42 which follows the score pattern indicated in FIG. 9. The scoring groove produced by the die operation is shown in cross section at 20 in FIG. 4.

It is contemplated that the scoring die will penetrate the sheet metal to substantially uniform depth so that the residual web of metal left by the scoring operation will be of minimum thickness in the annular zone around the hollow rivet where the sheet metal is of minimum thickness. Thus the residual web is thinnest at the leading end of the tear strip to facilitate initial severance of the tear strip. It is also to be noted that squeezing the sheet metal in the annular zone before the scoring operation work-hardens the metal to make the residual web relatively strong but at the same time somewhat brittle to favor initial severance of the tear strip.

Referring to FIG. 4, a tab 160 is shown resting on the upper surface of the can top blank 14a which blank has formed therein a rivet 18a of the initial configuration.

The tab 16a has an aperture therein, designated 16!). The rim of the aperture 16b may be beveled to avoid shearing or fracturing the face of the hollow rivet 18a when the hollow rivet is deformed into engagement with the tab.

FIG. 4 shows a lower die 44 and an upper die 45 which may be employed to head or deform the hollow rivet into permanent positive engagement with the tab 16a. The lower die 44 has a boss or upward projection 46 dimensioned to extend into the interior of the hollow rivet 18a to prevent axial collapse of the hollow rivet. The upper die 45 has a planar working face 48 which cooperates with the die boss 46 in the manner shown in FIG. 5.

FIG. 5 illustrates the relationship of the tab 16a, the can top blank 14a and the hollow rivet after the hollow rivet has been headed or deformed to the final rivet configuration 18 in permanent engagement with the tab.

In the die operation illustrated in FIG. 5, the upper die 45 cooperates with the boss 46 of the lower die to squeeze the transverse end wall of the rivet across its thickness and thereby causes the metal of the end wall to be extruded radially in all directions with the consequence that the rivet is expanded to form a head or hollow bead 47 on the rivet in overlapping engagement with the tab 16a.

Although the invention described herein may be used with a variety of metals, it is intended primarily for use with aluminum. The size of the can top blank 10 and the initial rivet 18a to be formed therein can be varied in accordance with the requirements of the finished product. The invention has been successful, for example, with. sheet aluminum .008 inches thick, using a die member 24 having a recess 34 therein of a diameter of .200 inches. The raised portion of plateau 28 of the die 22 was generally spherical and raised above the surface 26 by .0035 inches. The diameter of the plateau 28, as measured across the surface 26, was approximately .300 inches. The height of the initial rivet configuration 18a depends upon the degree of compression of the sheet metal and the area of plateau 28. The area of the annular working surface 32 of the upper die 24 was large in relation to the recess 34, as illustrated in FIGS. 2 and 3.

In FIG. 6, a die 22 is illustrated having a working surface somewhat different from that described above. In this case, a small circular boss 28a of curved cross section is formed centrally of the plateau 28 and co-axially of the upper die recess 34, the diameter of the boss being substantially smaller than the diameter of the recess. The result of the die operation illustrated in FIG. 6 is the same as the result of the previously described die operation illustrated in FIG. 3, but the boss 28a is advantageous in diverting the extruded metal upward into the recess 34.

The supports for the die have not been shown since such supports may be conventional. Actually, the formation of the initial rivet configuration 18a may be accomplished simply by striking the. upper die 24 with a hammer.

In the practice of the invention described to this point, the metal is squeezed in an annular zone around the base of the rivet by a die operation which indents the can top blank from its underside, i.e., from the side opposite to the side from which the hollow rivet protrudes. For this purpose the offset or plateau 28 that creates the squeezing action in the annular zone is on the lower die.

In the practice of the invention illustrated by FIGS. 7 to 11, the can top blank is indented on its upper side instead of on its under side, the plateau to create the annular compression zone being on the upper die instead of the lower die.

The lower die 50 in FIG. 7 has an insert 52 which forms a small central boss 54 which has the same function as the previously described boss 28a in FIG. 6. The upper die 55 in FIG. 7 has the usual recess 56 to provide a free space in which the hollow rivet may be formed. The upper die 55 has a working surface 58 to cooperate with the working surface 60 of the lower die 50 and the working surface 58 is offset towards the lower die to form an annular plateau 62 around the entrance to the recess 56.

At the limit closed position of the two dies shown in FIG. 7, the annular plateau 62 penetrates the sheet metal of the can top blank 14a and the remaining outer radial portion of the working surface 58 reaches a limit position which is spaced from the working surface 60 by the thickness of the can top blank. It is apparent that the squeezing of the sheet metal by the annular plateau 62 causes a hollow rivet to be formed of an initial configuration 18b shown in FIG. 8, the base of the hollow rivet being surrounded by an annular zone in the form of an indentation 64 on the upper side of the can top blank 14a. After the hollow rivet 18b is formed in this manner, scoring dies such as the previously described scoring dies are employed to form the usual score line 20. As may be seen in FIG. 9, the score line 20 enters the annular zone of annular indentation 64 and after passing around three sides of the hollow rivet 18b leaves the annular zone.

FIG. I0 shows how a tab 66 may be provided with the usual aperture 68 to receive the hollow rivet 18b and may be further provided with an annular offset 70 to nest into the annular indentation 64. FIGS. and 11 show how the hollow rivet at its initial configuration 18b may be deformed or headed into positive permanent engagement with the tab 66. For this purpose a pair of dies is used in the manner heretofore described, a lower die 72 being formed with a boss 74 to fit into the interior of the hollow rivet and an upper die 75 being provided with a planar working face 76. When the two dies close in the manner indicated in FIG. 11, the upper die 75 cooperates with the boss 74 to squeeze the end wall of the hollow rivet 18b thereby converts the hollow rivet to the final headed rivet 18.

A special advantage of the construction shown in FIG. Il may be understood by a comparison with the construction shown in FIG. 5. One of the problems in the design of a can of this type is to keep the hollow rivet from protruding above the plane of the rim or chime of the can. This problem is especially trouble some when the hollow rivet is in the central region of the can top and the can top is bulged outward by a pressurized content such as a carbonated beverage.

In FIG. 5 the whole of the circumferential bead of the rivet lies above the plane of the upper surface of the tab, whereas in FIG. 11 the fact that the tab is countersunk, i.e., formed with the annular indentation 64 permits the circumferential bead of the hollow rivet to extend partially into the plane of the tab. Thus the circumferential bead of the hollow rivet shown in FIG. 11 is lowered into the level of the tab to permit reduction in the length of the finished hollow rivet and corresponding reduction in the extent to which the rivet extends above the rest of the can top.

My description in specific detail of the selected embodiments of the invention will suggest various changes, substitutions and other departures from my disclosure within the spirit and scope of the appended claims.

I claim:

1. A method of forming a hollow rivet in a preselected segment of a can end of deformable metal for attachment of a tab to said can end, including the steps of:

pressurally engaging on opposite sides of the preselected segment a pair of die elements, the working face of one of which elements is formed with a recess of a predetermined cross-sectional size, to place the metal of a continuous zone of the segment engaged by said die elements under compressive stress sufficient to cause the metal of the zone and the metal of the segment circumscribed by said zone to be forcibly displaced into the recess with consequent thinning of the zone of the segment as the metal displaced flows into said recess to form an upstanding hollow rivet integral with said can end conforming to the cross-sectional size and shape of the recess of said one die element.

2. A method as defined in claim 1 wherein the working faces of said die elements are so formed that the metal displaced from said zone as said die elements are pressurally engaged on opposite sides of said segment results in the formation of an indentation extending inwardly from the same side of said segment as said rivet extends and circumscribing the base of said rivet.

3. A method as defined in claim I wherein the working faces of said die elements are so formed that the metal displaced from said zone as said die elements are pressurally engaged on opposite sides of said segment results in the formation of an indentation extending inwardly from the side of said segment opposite to the side from which said rivet extends.

4. A method of forming a hollow rivet in a preselected segment of a can end of deformable metal for the attachment of a tab to said can end, including the steps of:

placing a rigid support against one surface of the segment of said can end, and while holding said support in engagement with said one surface, impacting a die member having a working face circumscribing a recessopening into said face against the opposite surface of said segment with sufficient force to thin a zone of said segment engaged between said working face and said rigid support to displace metal thereof and metal of the portion of said segment circumscribed by said zone into said recess as a hollow protuberance with an end closing wall to form a hollow rivet integral with said can end conforming to the cross-sectional size and shape of said recess circumscribed'by the zone of reduced thickness from which metal was displaced in the formation of the rivet.

5. A method as defined in claim 4 wherein the metal displaced is directed toward the recess by providing a raised portion on saidrigid support member engageable with said one surface and generally coaxial with said recess, said raised portion extending radially outwardly of said recess.

6. A method as defined in-claim 4 wherein the flowing metal is initially directed into said recess by providing a raised portion on said rigid support engageable with said one surface, said raised projection being generally coaxial with and of smaller area than said recess.

7. A one-step method of forming a hollow rivet in a generally flat section of a can end of deformable sheet metal, said one step comprising:

coining the generally flat sheet metal of the section by compressively engaging die members on opposite sides of said section in a zone defined by the die members. 

1. A method of forming a hollow rivet in a preselected segment of a can end of deformable metal for attachment of a tab to said can end, including the steps of: pressurally engaging on opposite sides of the preselected segment a pair of die elements, the working face of one of which elements is formed with a recess of a predetermined cross-sectional size, to place the metal of a continuous zone of the segment engaged by said die elements under compressive stress sufficient to cause the metal of the zone and the metal of the segment circumscribed by said zone to be forcibly displaced into the recess with consequent thinning of the zone of the segment as the metal displaced flows into said recess to form an upstanding hollow rivet integral with said can end conforming to the cross-sectional size and shape of the recess of said one die element.
 2. A method as defined in claim 1 wherein the working faces of said die elements aRe so formed that the metal displaced from said zone as said die elements are pressurally engaged on opposite sides of said segment results in the formation of an indentation extending inwardly from the same side of said segment as said rivet extends and circumscribing the base of said rivet.
 3. A method as defined in claim 1 wherein the working faces of said die elements are so formed that the metal displaced from said zone as said die elements are pressurally engaged on opposite sides of said segment results in the formation of an indentation extending inwardly from the side of said segment opposite to the side from which said rivet extends.
 4. A method of forming a hollow rivet in a preselected segment of a can end of deformable metal for the attachment of a tab to said can end, including the steps of: placing a rigid support against one surface of the segment of said can end, and while holding said support in engagement with said one surface, impacting a die member having a working face circumscribing a recess opening into said face against the opposite surface of said segment with sufficient force to thin a zone of said segment engaged between said working face and said rigid support to displace metal thereof and metal of the portion of said segment circumscribed by said zone into said recess as a hollow protuberance with an end closing wall to form a hollow rivet integral with said can end conforming to the cross-sectional size and shape of said recess circumscribed by the zone of reduced thickness from which metal was displaced in the formation of the rivet.
 5. A method as defined in claim 4 wherein the metal displaced is directed toward the recess by providing a raised portion on said rigid support member engageable with said one surface and generally coaxial with said recess, said raised portion extending radially outwardly of said recess.
 6. A method as defined in claim 4 wherein the flowing metal is initially directed into said recess by providing a raised portion on said rigid support engageable with said one surface, said raised projection being generally coaxial with and of smaller area than said recess.
 7. A one-step method of forming a hollow rivet in a generally flat section of a can end of deformable sheet metal, said one step comprising: coining the generally flat sheet metal of the section by compressively engaging die members on opposite sides of said section in a zone defined by the working faces of said die members surrounding a given area in which the hollow rivet is to be formed and spaced radially inwardly of the periphery of said section to cause the metal of said zone to flow radially inwardly and upwardly into a recess formed in one die member and centrally opening onto the working face thereof to form a hollow rivet integral with said section of sheet metal circumscribed by the zone coined and thinned by said die members. 